Axial flow fans are well known in the art and conventionally consist of a number of blades supported by a central hub member, the blades being disposed regularly about the hub member. Some axial flow fans have a blade support linking together the tips of the blades, the blade support being an annular band. An especially important feature of axial flow fans in the context of vehicle cooling systems is the acoustic performance of the fans. Specifically, it is desirable to produce the quietest fans possible while at the same time providing both high efficiency and compact design.
A prior art patent, U.S. Pat. No. 5,312,230 discloses an axial flow fan aimed at improving efficiency by reducing the stagnant flow at the root of the blade. This prior patent uses arc-section blades having increased bending ratios as hereinafter defined in the root region.
The present invention seeks to reduce acoustic losses and thus to provide both improved noise performance and efficiency.